Leverage systems are known which comprise a load arm connected at one end to a linkage network and at an opposite end to a gripper. The gripper holds any of a variety of tools for performing such diverse operations as loading and unloading, drilling, welding, lacquering, etc., while the linkage network is pivotally mounted on a vertically rotatable base for enabling the support of the gripper at nearly any location within a hemisphere. Such a leverage system has a weight-compensating assembly for counterbalancing the gravitational moment tending to swing the linkage network, the load arm and the gripper about the horizontal axis. Usually the weight compensator includes a pressure device for applying to the linkage network a force substantially proportional to the extension of the leverage system, the pressure device having a piston pivotally secured to a lever which is rigid with a so-called horizontal member of the linkage and which is swingable with this member about a pivot on the base (see German patent DE-OS 27 01 151).